Well plates for holding samples, and in particular, liquid samples, such as bodily fluids, for example, blood, blood plasma, urine and other such bodily fluids during analysis in analytical apparatus are known. Typically, such well plates comprise a plate having a plurality of wells located therein in which the samples to be analysed are placed, typically, by pipetting into the wells from a vial or vials containing the samples. Such well plates may comprise an elongated strip plate which may be of flexible, semi-rigid or rigid material having a plurality of wells located therein arranged in a single column extending longitudinally along the strip plate. Alternatively, the well plate may comprise a plate having the wells arranged in a matrix formed by a plurality of rows and columns of the wells. Typically, the well plate is adapted for use in a particular analytical apparatus in which the samples are to be analysed.
The wells may be of a type which are adapted for optical analysis whereby light is directed at or through the sample in the well, and the spectrum of the light reflected from or transmitted through the sample is analysed in order to determine a characteristic of the sample, for example, a characteristic which would indicate the state of health of a subject from whom the sample of bodily fluid was obtained.
Alternatively, the wells may be of the type which are adapted for carrying out a mechanical analysis of a sample. Such mechanical analyses, in general, are carried out by determining the viscosity of the sample. Many mechanical methods are known for use in analytical apparatus for determining sample viscosity. A particularly common method is based on determining the speed at which a ball travels through the liquid sample. Typically, the ball is of steel or another suitable magnetically sensitive material, and is energised to move through the sample by applying a magnetic field externally of the well. The viscosity of the liquid sample is determined by comparing the speed with which the ball moves through the sample with the strength of the energising magnetic field.
Such known well plates are adequate for carrying out optical and mechanical analysis where the accuracy of the sample size which is placed in the well is not critical. However, where the sample size is critical, such well plates are unsuitable. This is as a result of the fact that, in general, the sample is transferred to a well in the well plate by pipetting from a vial containing the sample. Such vials typically are closed by a stopper of a rubber or rubber type plastics material. Pipetting of the sample from the vial to the well in the well plate is carried out by piercing the stopper of the vial with a pointed cannula which is then inserted through the stopper into the vial, and a volume of the sample is withdrawn into the cannula. However, due to the fact that the vial is closed by the stopper during pipetting of the sample, the pressure within the vial may vary above or below atmospheric pressure as a result of temperature, and indeed, the mere insertion of the stopper in the vial when closing the vial may be sufficient to increase the pressure within the vial above atmospheric pressure. Accordingly, variation in pressure within the container from which the sample is being pipetted results in a variation of the sample size withdrawn from the vial by pipetting. This is unsatisfactory where the sample size is critical.
Another problem with well plates known heretofore is that in general, the wells are unsuitable for mixing a sample with a reagent.